1. Field of the Invention
The present invention relates to computer storage systems, and, more particularly, to file servers or Network Attached Storage (NAS) systems having NFS version 4 functionality.
2. Description of the Related Art
Historically, to share files with multiple hosts, protocols such as NFS (Network File System) protocol version 2 or 3 have been used. NFS is a distributed file system and associated network protocol originally developed by Sun Microsystem Computer Corporation, although the IETF (Internet Engineering Task Force) is now responsible for the NFS standard.
In previous and current NFS versions 2 and 3, a name space (or directory tree) of a file system is constructed within each server. Therefore, when a file system on a first server is migrated to a new server, clients themselves must change their target to send requests to the new server to access the migrated file system on the new server.
Recently, NFS version 4 has been proposed, and is being developed and implemented on several platforms. In NFS version 4, the name space of a file system can be constructed over multiple servers utilizing referrals. Referrals are the attributes that inform clients of a new location of a file system. When a file system on an old server is migrated to a new server, and when a  client attempts to access the file system on the old server, the client is notified of the new location of the file system by a referral so that the client can redirect the access request to the new server. Therefore, clients can access the file system transparently (without being concerned about the new location of the file system) even after the file system is migrated to another server. This feature is called “Global Name Space”, and the file system having this feature is called a “Global File System”.
Additionally, data replication techniques such as remote copy are often used in storage systems in preparation for situations where the original data is lost or corrupted. Remote copy is a technique to keep a synchronized or asynchronous copy of a file system in a remotely-deployed file server or NAS (Network Attached Storage) system. Conventionally, the remote copy technique is used to copy a file system on a single file server to a single remote file server because each file system can be constructed only within each server.